Unwanted Subwoofer noise from AVR?
Hi, I've had a problem with subwoofer noise from my receiver, a brand new Denon avr-x4000.
I have a pair of subwoofers driven by a behringer EP2500, the behringer is connected directly to the pair of RCA subwoofer outs on the receiver so there is no physical in-line crossover or LPF. (which I know might solve the issue, but It's still an issue I'd like to know more about)
There is an audible noise coming from the actual sub drivers, but not a hum, it's hard to describe but I'd say it's like a dull electrical crackle, a bit like the test tone rumble but not in the bass frequency range.
It's not loud but it does increase with the receiver volume so I think it's the receiver which is causing the noise, when a silent section between two songs occurs I can hear it quite clearly at med-high volume.
Does anyone have any clue what this noise could be caused by?
It's not present on the main powered speakers, just the subs and it's much more evident on one of the subwoofer outputs than the other (I did some cable swapping)
I've made a short recording of the noise, I was testing on optical input and I've noticed if I unplug the Optical cable (fed from PC sound card) the sound goes away for a few seconds but then after 3-4 seconds the amp detects a change, makes the relay 'click' and the funny sound comes back but twice as loud!
For control, this was done with a different amplifier and speaker but from the same "Subwoofer 1" output (which is the noisiest of the two)
20131109_155912.mp4 - YouTube
I used an old BK elec MF 300 amplifier and Tannoy speaker to eliminate the behringer/subs being the issue.
The results are identical on both set-ups.